The present application relates generally to an apparatus for charging one or more batteries. More specifically, it relates to an apparatus for charging one or more batteries in an uniterruptible power supply system.
Generally, uninterruptible power supply (UPS) systems and DC storage plants are set up with batteries directly connected to a bus only through fuses, switches, relays, or shunts. For example, FIG. 1 shows a typical prior art uninterruptible power supply UPS system 10. A charger 12 or rectifier is coupled between an input 14 having alternating current and a DC bus 16 and converts the alternating current to a direct current. Multiple battery packs 18a-18c are connected to the DC bus 16 and are thus charged by the charger 12. The DC bus 16 is connected to an inverter 20, which is connected to the UPS output 22. A system bypass 24 can also be included for bypassing the UPS system in the event of a UPS malfunction. In the event of a power failure from input 14, the batteries 18a-18c will supply power to the UPS output 22 through the inverter 20.
FIG. 2 shows a typical prior art UPS system in a DC storage plant. One or more rectifiers 32a, 32b are respectively coupled between inputs 34a, 34b each having an alternating current signal thereon and a DC bus 36 and convert each alternating current signal to a direct current. Multiple battery packs 38a-38c are connected to the DC bus 36 and are thus charged by the rectifier 32. The DC bus 36 is connected to one or more inverters 40a, 40b, which are respectively connected to the UPS outputs 42a, 42b. Like the UPS system of FIG. 1, in the event of a power failure from input 34a and/or 34b, the batteries 38a-38c will supply power to the outputs 42a, 42b. 
In both FIGS. 1 and 2, there is no control over the flow of energy in and out of the batteries because they are connected directly to the DC bus. In these systems, if a discharged battery is connected to the bus, the other batteries will deliver energy to the discharged battery until its charge is the same as all the rest, assuming that the voltage versus charge characteristics of all batteries are the same. Moreover, the systems in both FIGS. 1 and 2 do not allow for individualized dynamic charge control of each energy storage device so that dissimilar energy storage devices, such as batteries of different chemistry, and storage devices of similar type but differing condition, such as batteries in different temperature zones or of differing ages, cannot effectively be connected to the same bus.
Embodiments of the present invention use a power regulator, such as a DC to DC converter, connected between one or more energy storage devices and a DC bus to control the energy flow of each of the energy storage devices in a desired manner. In one embodiment of the invention, the system for controlling multiple energy storage devices in an uninteruptible power supply (UPS) system includes a charger coupled to a direct current (DC) bus of the UPS system, and two or more energy storage circuits each of which include a power regulator coupled to the charger and coupled to the DC bus, at least one energy storage device coupled to the power regulator; and a processor coupled to the converter for controlling the charge and discharge of the at least one energy storage device.
In another embodiment of the invention, a digital communication link such as that employing the Control Area Network (CAN) protocol is used to digitally communicate between two or more processors. Communication using the CAN protocol can be accomplished over the DC bus or can be accomplished over an additional copper, fibre-optic or wireless communication link.
In yet another embodiment of the invention, the energy capacity of the system is determined though a voltage measurement of the DC bus which is set by the one or more energy storage devices to be equal to a value representing the collective energy stored/remaining according to a predetermined voltage to capacity relationship.
One advantage of embodiments of the invention is that the energy storage devices will regulate their discharge and recharge rates according to predetermined system requirements and their own capability.
Another advantage of embodiments of the invention is that the energy capacity of the system can be determined by simply measuring the voltage on the DC bus. By measuring the voltage of the DC bus, an inverter, which typically has no information as to how many battery packs are coupled to it, can easily tell how much run-time it has without digital communication to a master controller. Devices that draw energy from the bus, such as load equipment, can obtain information about the remaining run-time. This information is particularly beneficial when the master controller is unavailable or not installed or when digital communication is unavailable.
Yet another advantage of embodiments of the invention is that the energy delivery system can be designed with the more versatile digital communication system and have a reliable back-up communication system in case the digital communication is unavailable merely by measuring the voltage on the DC bus.